Wood preservatives

ABSTRACT

A wood preservative composition and method for preserving wood by contacting wood with said composition comprising a polyurethane polymer, non-aqueous solvents, and a wood preservative active.

The present invention relates to a wood preservative composition and method for preserving wood to impart protection from wood-decaying organisms.

There are many methods and compositions for preserving wood prior to the time the wood is put in use. Also, preservatives for treating wood in place are available on the market including both oil-based and water-based products. The oil-based products generally consist of petroleum oils with pentachlorophenol or creosote. U.S. Pat. No. 7,959,723 describes one such composition employing oil-soluble preservatives for wood. From the standpoint of toxicity and environmental pollution, these active ingredients are less than desirable.

The problem addressed by this invention is the need for a more environmentally friendly wood treatment composition which is capable of efficaciously imparting active ingredients.

The present invention is directed to a method for preserving wood comprising contacting wood with a wood preservation composition comprising a polyurethane polymer synthesized from a polyol comprising >95% p-propylene oxide, and an isocyanate; an organic solvent; and at least one wood preservative active selected from among halogenated isothiazolone biocides, halogenated carbamate fungicides and azole fungicides; wherein the isocyanate to polyol molar ratio of the polyurethane polymers is from less than or equal to 0.8 to greater than or equal to 0.1.

The present invention is further directed to a wood preservation composition comprising a) a polyurethane polymer synthesized from a polyol comprising >95% p-propylene oxide; and an isocyanate, b) an organic solvent; and c) at least one wood preservative active selected from among halogenated isothiazolone biocides, halogenated carbamate fungicides and azole fungicides; wherein the isocyanate to polyol molar ratio of the polyurethane polymers is from less than or equal to 0.8 to greater than or equal to 0.1.

All percentages and part per million (ppm) values are on the basis of total weight of the composition, unless otherwise indicated. The terms “a” or “an” refer both to the singular case and the case where more than one exists. All range endpoints are inclusive and combinable. As contained herein all molecular weights are number average molecular weight and are determined by Gel Permeation Chromatography (GPC). It is envisioned that one skilled in the art could select and/or combine multiple suitable and/or preferred embodiments in the present invention.

The wood preservative compositions of the present invention comprise polyurethane polymers that are synthesized from a stoichiometric excess of bis hydroxy terminated polypropylene oxide macromere (polyol) and an isocyanate. Polyurethane polymers, as used herein, may contain other functional groups derived from reaction of isocyanates with other monomers, e.g., amide groups derived from carboxylic acids, and ureas derived from amines, e.g. ethylene diamine (EDA) or other polymers, such as polyesters, e.g., polyesters derived from adipic acid and 1,6-hexanediol, 1,4-butanediol and/or neopentyl glycol, or polycarbonates, e.g. polycarbonates derived from poly 1,6-hexanediol carbonate. Suitable isocyanates include, e.g., methylene bis(4-cyclohexylisocyanate) (MCI), methylene bis(4-phenylisocyanate) (MDI), polymethylenepolyphenol isocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and toluene diisocyanate (TDI) and combinations thereof. Preferably, the isocyanates of the present invention are diisocyanates. Examples of suitable diisocyanates include IPDI, pMDI, MDI and combinations thereof. More preferably, the diisocyanates are MDI and IPDI. The polyol used to make the polyurethane in the present invention is >95% p-propylene oxide. Suitably the isocyanate to polyol molar ratio of the polyurethane polymers is from less than or equal to 0.8 to greater than or equal to 0.1.

The polyurethane polymer is synthesized in a non-aqueous solvent or a mixture of non-aqueous solvents. Preferably, the amount of solvent is from 60% to 90%, more preferably from 70% to 90%, and most preferably from 75% to 90%. Suitable solvents include ester and ether solvents having a boiling point of at least 150° C., and preferably a flash point of at least 60° C. Examples of such solvents include, alkanes, branched alkanes, aromatics, e.g., Mineral spirits, toluene, benzyl alcohol, xylenes, and alkyl benzenes. A suitable mixture of non-aqueous solvents useful in the present invention is Aromatic 200, CAS No. 64742-94-5.

The wood treatment composition of the present invention, in addition to polyurethane polymer, further comprises a wood preservative active. The wood preservative active may be selected from the class of halogenated isothiazolinone biocides, halogenated carbamate fungicides, metal salts of naphthenic acids, and azole fungicides. When the wood preservative active is a halogenated isothiazolinone biocide, it preferably comprises a 3-isothiazolone having a C₄-C₁₂ N-alkyl substituent, more preferably a chlorinated 3-isothiazolone, and most preferably 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (“DCOIT”). Mixtures of wood preservatives actives may be used. When the polyurethane polymer is combined with DCOIT a suitable composition includes 23% polyurethane polymer solids, 23% DCOIT, and 54% Aromatic 200.

The composition used to treat wood preferably contains from 100 ppm to 40,000 ppm wood preservative, more preferably from 200 ppm to 30,000 ppm, and most preferably from 300 ppm to 25,000 ppm. Preferably, the polymer solids content of the composition is from 10% to 40%, more preferably from 10% to 30%, and most preferably from 15% to 30%. Preferably, the polymer solids to biocide ratio is from 2:1 to 1:2, more preferably from 2:1 to 1:1.

Another critical element of the wood preservation composition is an organic solvent. The polyurethane polymer is diluted with organic solvent. Suitably, the organic solvent is diesel, however other organic solvents known to those of skill in the art may be used. In some embodiments the organic solvent is not the same compound as the non-aqueous solvent of the present invention. As used herein, diesel is defined as the fractional distillation of crude oil between 200° C. (392° F.) and 350° C. (662° F.) at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 8 and 21 carbon atoms per molecule or biodiesel that is obtained from vegetable oil or animal fats (biolipids) which have been transesterified with methanol (fatty-acid methyl ester (FAME)) and mixtures thereof.

The compositions used in the present invention may optionally contain additional components including but not limited to stabilizers, dyes, water repellents, other wood biocides, fungicides and insecticides, antioxidants, metal chelators, radical scavengers, etc. Stabilizers include, e.g., organic and inorganic UV stabilizers, such as, copper oxide or other copper salts or complexes that resist leaching; zinc oxide; iron salts, iron oxide, iron complexes, transparent iron oxide and nanoparticle iron oxide; titanium dioxide; benzophenone and substituted benzophenones; cinnamic acid and its esters and amides; substituted triazines, such as triphenyl triazine and substituted phenyl triazine UV absorbers, benzotriazole and substituted benzotriazole UV absorbers; hindered amine light stabilizers, used individually or in combination. Water repellents include, e.g., various wax-type water repellents, e.g., paraffin, carnauba, and polyethylene waxes; and silicones. Other wood biocides, fungicides, such as copper metal, bethoxazin and cyproconazole, chlorothalonil, tebuconazole, propiconazole, pentachlorophenol, creosote, copper napthenate, dialkyl dimethyl quaternary ammonium carbonate/bicarbonate, and insecticides include, e.g., those listed in U.S. Pat. No. 6,610,282, e.g., imidacloprid, thiacloprid, permethrin, and etofenprox. Antioxidants include any commercially available antioxidant compounds, e.g., phosphite antioxidants such as IRGAFOS; lactone antioxidants; phenolic antioxidants such as BHT; ascorbic acid; and IRGANOX and the like. Metal chelators include, e.g., EDTA, NTA, 1,10-phenanthroline, ACUMER 3100, DEQUEST, TAMOL 731, tripolyphosphate and other inorganic and organic compounds and polymers useful in chelating or dispersing metal salts. Radical scavengers include, e.g., TEMPO.

Preservation of wood is performed by contacting the wood with the wood preservation composition described herein, preferably under conditions that comply with AWPA Standards T1-16 and meet conditions for use specified in U1-16. In order to provide long term protection, the preservative needs to “fix” in the wood and not deplete too rapidly by volatilization or by leaching when the wood gets wet. It might be expected that enhanced penetration or enhanced movement of the preservative deep into the wood during treatment might also lead to reduced fixation of the organic wood preservative active.

EXAMPLES Synthesis of Polyurethane Polymers:

The following polyurethanes were synthesized from a stoichiometric excess of bis hydroxy terminated polypropylene oxide (polyol) and an isocyanate. 150 mL of anhydrous polypropylene oxide in aromatic 200 (solvent, 10-30 wt % solution) and isocyanate (0.8 molar equivalents of isocyanates to hydroxyl groups), was charged with 0.003% of a Tin catalyst (dibutyltin dilaurate) to the reactor. The reactor was heated to 90° C. with overhead stirring. The reaction mixture was held at 90° C. for 3 h and at that time point no free isocyanate was observed when tested with SWYPEs™ test strips. The polymer solids of the PU solution was estimated from the conversion and the amount of reactants used for the reaction. The polymer solids are calculated as the sum of the reactive components in the synthesis of the polymer.

Comparative samples 1 to 6 and Examples 2-4 were synthesized following the sample procedure above except that the NCO/OH molar ratio was changed. Comparative samples 7 to 9 and Examples 5-8 were synthesized following the sample procedure except that MDI is used instead of IPDI and NCO/OH molar ratio varied.

Procedure to Determine Diesel Compatibility:

In a clear, 1 oz vial, 0.1 gram of the polymer (on a 100% polymer solids basis) is diluted with 9.9 grams of diesel fuel (weight/weight) to a 1% solution of the polymer. The sample is maintained at room temperature for 48 hours. After 48 hours, the solution is checked for incompatibility, defined as phase separation, precipitation of the polymer as solids, and/or turbidity.

TABLE 1 Diesel Compatibility of PU Polymers with 100% p-iPO with IPDI Diesel compatibility (1 wt. %) Polyol Polyol Polyol Polymer Polyol Isocyanate (NCO/OH MW = MW = Mw = # (bis OH) (Bis NCO) molar ratio) 2000 2700 4000 Comp. 1 P4000 IPDI 2 No No No (p-iPO) Comp. 2 P4000 IPDI 1.5 No No No (p-iPO) Comp. 3 P4000 IPDI 1.1 No No No (p-iPO) Comp. 4 P4000 IPDI 1 No No No (p-iPO) Comp. 6 P4000 IPDI 0.9 No No No (p-iPO) Ex-1 P4000 IPDI 0.8 Yes Yes Yes (p-iPO) Ex-2 P4000 IPDI 0.5 Yes Yes Yes (p-iPO) Ex-3 P4000 IPDI 0.25 Yes Yes Yes (p-iPO) Ex-4 P4000 IPDI 0.1 Yes Yes Yes (p-iPO)

TABLE 2 Diesel Compatibility of PU Polymers with 100% p-iPO with IPDI Diesel compatibility (1 wt. %) Polyol Polyol Polyol Polymer Polyol Isocyanate (NCO/OH MW = MW = Mw = # (bis OH) (Bis NCO) molar ratio) 2000 2700 4000 Comp. 7 P4000 MDI 2 No No No (p-iPO) Comp. 8 P4000 MDI 1.5 No No No (p-iPO) Comp. 9 P4000 MDI 0.9 No No No (p-iPO) Ex-5 P4000 MDI 0.8 Yes Yes Yes (p-iPO) Ex-6 P4000 MDI 0.5 Yes Yes Yes (p-iPO) Ex-8 P4000 MDI 0.1 Yes Yes Yes (p-iPO) 

1. A method for preserving wood comprising: contacting wood with a wood preservation composition comprising a) a polyurethane polymer synthesized from i) a polyol comprising >95% p-propylene oxide, and ii) an isocyanate b) an organic solvent; and c) at least one wood preservative active selected from among halogenated isothiazolone biocides, halogenated carbamate fungicides and azole fungicides; wherein the isocyanate to polyol molar ratio of the polyurethane polymers is from less than or equal to 0.8 to greater than or equal to 0.1.
 2. The method of claim 1 in which the wood preservative active is 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one.
 3. The method of claim 1 wherein the organic solvent comprises diesel.
 4. The method of claim 1 wherein the polyol comprises 100% p-propylene oxide.
 5. The method of claim 1 wherein the isocyanate is methylene bis(4-phenylisocyanate.
 6. The method of claim 1 wherein the isocyanate is isophorone diisocyanate.
 7. A wood preservation composition comprising a) a polyurethane polymer synthesized from i) a polyol comprising >95% p-propylene oxide, and ii) an isocyanate b) an organic solvent; and c) at least one wood preservative active selected from among halogenated isothiazolone biocides, halogenated carbamate fungicides and azole fungicides; wherein the isocyanate to polyol molar ratio of the polyurethane polymers is from less than or equal to 0.8 to greater than or equal to 0.1. 